FIG. 1 depicts a plan view of a conventional array 10 of magnetic recording heads formed on a wafer, or substrate, 12. The conventional array 10 includes heads 14 that are formed in rows. Although only six rows of five, eleven, or fourteen heads are shown, typically a larger number of rows and a larger numbers of heads 14 per row are fabricated. The heads 14 include write transducer and read transducers. The write transducers may be perpendicular magnetic recording (PMR), energy assisted magnetic recording (EAMR), or other writers. The read transducers typically include tunneling magnetoresistive (TMR) or other analogous read sensors.
FIG. 2 depicts a conventional method 50 for testing the heads 14. For simplicity, only a portion of the method 50 is described. The wafer 12 is heated to a desired temperature, via step 52. Step 52 may include placing the entire wafer 12 in a furnace. The furnace may then be set to the desired temperature, and time allowed for the temperature of the wafer 12 to equilibrate. Alternatively, if cooler temperatures are desired for testing, step 52 could include cooling the wafer 12 to the desired temperature. Test(s) may be performed on the heads 14 using the desired temperature, via step 54. For example, the magnetoresistance or other properties at particular temperatures might be determined. Steps 52 and 54 may then be repeated for a variety of temperatures.
Although the heads 14 may be fabricated in a conventional array 10 and tested using the method 50, there are significant drawbacks. Many of the tests desired to be performed for the heads 14 are destructive. At least some of these tests are desired to be performed on-wafer. An on-wafer test is one which is performed with most or all of the devices 14 remaining on the wafer 12 during the test. Once these destructive tests are performed in on-wafer testing, the heads 14 can no longer be placed in devices to be used and/or sold. For example, the blocking temperature (Tb) and distribution in the blocking temperatures (TbD) of the TMR sensors in the heads 14 may be desired to be known. These can be determined using the method 50. To do so, the wafer is heated in step 52. In step 54, a magnetic field is applied while the wafer 12 is at the elevated temperature, the wafer is then cooled to room temperature, and the transfer curve of the TMR sensor is determined for the magnetic field applied at that elevated temperature. More specifically, the resistance versus field is determined at room temperature for each read sensor in each head 14. Once the temperature to which the wafer 12 is heated in step 52 exceeds the blocking temperature of the TMR sensor, the shape of the transfer curve changes. Thus, the blocking temperature can be determined for the heads 14. However, because the heads 14 have been heated above the blocking temperature, the read sensors in the heads 14 may be damage. As a result, the heads 14 are no longer usable. Thus, the heads 14 for which the most information is known can no longer be placed in devices. Further, if there are variations between wafers, the method 50 may not adequately capture these variations or allow prediction of the characteristics of heads on other wafers. Even if separate test structures (not shown in FIG. 1) are placed on the wafer 12, the method 50 is still used to test the heads 14. Thus, the same issues relating to damage of the heads 14 are still faced.
Accordingly, what is needed are improved methods and systems for testing arrays of heads.